Commercial and Military Laser devices generally use mechanically controlled (gimbaled) mirrors to aim, steer, and scan laser beams. Such mechanically controlled systems have several disadvantages: (1) weight, (2) size, (3) power consumption, (4) mechanical breakdown, and (5) time delays in steering. Considerable resources have been spent by commercial and military research to find acceptable alternatives to this gimbaled approach which can also cover wide fields of regard with high accuracy “fine” beam pointing.
Two promising approaches to eliminate the mechanical gimbals have been developed in the last decade. One approach uses a Steerable Electro-Evanescent Optical Refractor (SEEOR) continuous steerer for fine beam control, e.g. as described in U.S. Pat. No. 8,311,372, Anderson et al., issued Nov. 13, 2012, and U.S. Pat. No. 8,463,080, Anderson et al., issued Jun. 11, 2013, both of which are incorporated herein by reference. The other approach, described in J. Kim, C. Oh, M. J. Escuti, L. Hosting, and S. A. Serati, “Wide-angle, nonmechanical beam steering using thin liquid crystal polarization gratings,” Advanced Wavefront Control: Methods, Devices, and Applications VI (SPIE, 2008) (the “PG approach”), employs a series of polarization gratings (“PG”s) to discretely cover a wide field of regard. Each of these techniques, however, have limitations to completely (continuously) cover a wide field of regard with no dead spots. The SEEOR approach requires an enormous number of liquid crystal prisms to cover a wide field of regard although each SEEOR refractor does an excellent job of fine beam control within a narrower field of regard (as much as 60°×15°) The PG approach easily obtains a wide field of regard but requires many layers to get to high resolution fine tracking since it discretely splits the field of regard in two—hence 12 PG layers will get 4096 fine-resolution beam positions.